Question

Light travels fastest in

• A. Air
• B. Water
• C. Glass
• D. Diamond

Answer 1

The correct option is A

Air

Speed of light:

The value for the speed of light in a vacuum is now defined exactly as $299792458\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$.

Explanation:

1. Light waves travel fastest through the air, and slower through other materials such as glass or water.
2. Speed of light in a medium of refractive index $n$ is given by:
   $v=\frac{c}{n}$, or $v\propto \frac{1}{n}$ Hence, for more $v$, $n$ should be less.
   $v=$speed of light in the medium, $c$= speed of light in vacuum
3. Among the given options, the refractive index of air is less.
4. Hence, the light will travel faster in the air.

Thus, the correct option is option A.